Assessing Trade-Offs of Thermal Resilience
Although increases in the relative abundance of Durusdinium trenchii (formerly known as Symbiodinium D1a) in corals due to symbiont shuffling may increase thermal tolerance, this shift may cause trade-offs that impact the viability of symbiont shuffling at the ecosystem scale (Ortiz et al. 2013). It is possible that corals will gradually lose D. trenchii in the absence of thermal stress. Several studies have shown decreased calcification or growth rates in corals dominated by D. trenchii (Little et al. 2004, Jones & Berkelmans 2010, Pettay et al. 2015) suggesting that while this symbiont increases a coral's heat tolerance, it may also lead to slower reef growth and reduced competitive ability.
One study showed that colonies hosting Durusdinium exhibited decreased incidence of disease, suggesting that D. trenchii may decrease a host's susceptibility to disease (Correa et al. 2009). However, the bleaching process that often leads to Durusdinium dominance may also temporarily weaken the coral and increase susceptibility. As such, future studies need to unravel the relationships between bleaching, symbiont shuffling, and disease susceptibility.
Part of my research involves assessing possible eco-physiological trade-offs in manipulated coral recruits outplanted to reefs. After outplanting coral recruits with Durusdinium and with other dominant symbiont types, I will compare survivorship, growth rates and disease susceptibility in the field over a period of two years. Ultimately, these data will help me understand whether Durusdinium gives a long-term advantage to coral juveniles in the face of multi-faceted and changing ocean conditions.